Viscous liquids such as drink concentrate and syrups often need to be measured out fairly precisely, too much concentrate may make a drink too strong and too little, too weak. Often it is hard to ascertain exactly how much syrup needs to be added due to the different viscosities. The ideal amount for one flavor may not be so optimal for another. Also it is often difficult to assess how much syrup has been dispensed especially when a bottle or container is almost empty and the last drops are being shaken out. If a bottle containing syrup is shaken too hard, too much syrup is released etc.
The manual addition of these syrups may also be messy especially when adding them to a vessel with a small opening such as the addition of syrup to a bottle of carbonated water. Particularly viscous syrups may not just flow though the mouth of the bottle but also down the sides.